Well, I for one found the Lightfoot Test Of Strength really hard (The Krazoa version of it had to be the easiest thing in the game practically.), and I found the Test Of Fear and the Final Battle really hard. I recall nearly throwing my controller at the screen because of those...but I would just take a sip of water, and take a few deep breaths, and I was all set

Ah, you mean the Red Eye King. He isn't that hard once you figure out what to do, and you get the hang of it

I got up to the last boss, and boy, it took me a while to beat him. I finally figured out that if I just put the controller on a chair, and stayed in one spot, shooting the asteroids as they came out of the boss' mouth, instead of trying to dodge them, I could beat him pretty easily.